In magnetic storage systems, data is read from and written onto magnetic recording media utilizing magnetic transducers commonly. Data is written on the magnetic recording media by moving a magnetic recording transducer to a position over the media where the data is to be stored. The magnetic recording transducer then generates a magnetic field, which encodes the data into the magnetic media. Data is read from the media by similarly positioning the magnetic read transducer and then sensing the magnetic field of the magnetic media. Read and write operations may be independently synchronized with the movement of the media to ensure that the data can be read from and written to the desired location on the media.
In a tape drive system, magnetic tape is moved over the surface of the tape head at high speed. This movement generally entrains a film of air between the head and tape. Usually the tape head is designed to minimize the spacing between the head and the tape. The spacing between the magnetic head and the magnetic tape is crucial so that the recording gaps of the transducers, which are the source of the magnetic recording flux, are in near contact with the tape to effect efficient signal transfer, and so that the read element is in near contact with the tape to provide effective coupling of the magnetic field from the tape to the read element.
Magnetic tape may use a written servo pattern to indicate lateral position on tape. This servo pattern is used to indicate lateral position, on tape, of the various written tracks. The servo pattern is not perfect due to variations in tape velocity and lateral position in the servo writer during servo writing. This can partly be attributed to the inability of most mechanical head positioning motors to react to tape lateral position changes fast enough to move the head into proper position to write the servo pattern. The component of the servo pattern due to the velocity variations and lateral motion is termed the ‘written in’ component and limits the accuracy of the track-following actuator in the drive. This is due to the high frequency components of the ‘written in’ servo which the track-following actuator has difficulty in following. Greater track-following accuracy becomes more important as written tracks get narrower. Hence ‘written in’ servo noise limits the ultimate track pitch attainable in magnetic tape recording.